Method of imparting flame-resistance to cellulosic materials



awrrateei Unitec NETHGD or IMPARTING FLAME-RESISTANCE 'ro CELLULOSIC MATERIALS Anne MacMillan Loukomsky, North Plainfield, N. 1., assignor to American Cyanamid Company, New York, N. Y., a corporation of Maine No Drawing. Application April 11, 1950, Serial No. 155,353

3 Claims. (Cl. 117-136) This invention relates to a method of imparting flame resistance to cellulosic fibrous material such as cotton and regenerated cellulose, cellulose ester or cellulose ether yarns, threads, and fabrics, paper, paper board and other relatively porous combustible materials composed of or containing cellulose by incorporating flame-resistant compositions therein. The invention includes improved flameresistant compositions composed of or containing guanylmelamine pyrophosphates, their methods of application to fibrous cellulosic material, fibrous cellulosic materials so treated, and further improvements resulting in greater permanency of the flame-resistant material against removal by dusting, washing or abrasion as will hereinafter be described.

I have found that the salts of guanylmelamine with pyrophosphoric acid, which are hereinafter designated as guanylmelamine pyrophosphates, possess to a high degree the property of inhibiting flame propagation in fibrous cellulosic materials of the above described types. My present invention, therefore, consists in the method of imparting flame resistance to cellulosic fibrous material by incorporating guanylmelamine pyrophosphates therein, either alone or in admixture with resinous binders, and in the flame-resistant cellulosic materials so obtained.

Guanylmelamine is most easily prepared by reacting dicyandiamide with substantially anhydrous hydrogen chloride at temperatures between 55 -180 C. and preferably between 100l50 C. The reaction may be carried out in an anhydrous solvent such as phenol if desired. The guanylmelamine hydrochloride so obtained may be used directly in carrying out the flame proofing process of the present invention.

Although the guanylmelamine pyrophosphates are insoluble in Water they may have a tendency to separate from the cellulosic textiles, paper or other material by dusting. I have found that the guanylmelamine pyrophosphates Will impart flame resistance to organic binders of the type of aminotriazine-aldehyde resins, ureaaldehyde resins, and phenol-aldehyde resins and even (with larger quantities) to alkyd resins, and therefore these binders may be used to prevent dusting or other forms of mechanical separation of crystalline guanylmelamine pyrophosphates from the-fibrous cellulosic material. It should be understood, however, that the proper quantity of guanylmelamine pyrophosphate to impart flame-resistan'c'e to the binder (about 15-30% with melamine-formaldehyde resin binders, based on the weight of the resin) must be added in addition ,to the amounts employed to give flame resistance to the cellulosic textiles or other types of fibrous cellulosic material.

The water-insoluble guanylmelamine pyrophosphates may be applied to the fibrous cellulosic material by impregnating the fibrous cellulosic material with a watersoluble salt such as guanylmelamine hydrochloride, followed by treatment of the impregnated material with pyrophosphoric acid or a water-soluble salt thereof.

Although a wide variety of resinous binders may be Patented Jan. 29, 1957 phosphates from the fibrous cellulosic material, I prefer to' employ the resinous amino-triazine-aldehyde condensation products for this purpose. Aqueous solutions or syrups of hydrophilic aminotriazine-aldehyde condensation products such as melamine-formaldehyde resins have given good results in practice but the organic solventsoluble types, obtainable by reacting methylol melamines or other primary aminotriazine-aldehyde condensation products with alcohols such as butanol, octanol and the like in the presence of small quantities of acidic etherifica tion catalysts such as oxalic acid or phthalic anhydride, may be used. Urea-formaldehyde condensation products such as dimethylol urea or methylated dimethylol urea may also be used if desired. My preferred resinous binder, however, is the water-soluble type of methylated methylol melamine, prepared by reacting a melamineformaldehyde condensation product with methanol in the presence of a very small quantity of a mildly acidic catalyst followed by neutralization of the catalyst when the esterification has been completed.

The above and other resinous binders may be applied as a separate after-treatment to the cotton cloth or other fibrous cellulosic material containing the guanylmelamine pyrophosphate formed by precipitation or the guanylmelamine pyrophosphate may be suspended in the resin solution and applied in a single operation. In the latter method of application the methylated methylol melamines are particularly useful as binders, since they are resistant to precipitation upon the addition of guanylmelamine pyrophosphates and therefore the treatment baths will remain stable for considerable periods of time.

The quantity of guanylmelamine pyrophosphate to be employed may vary within wide limits depending on the type of fibrous cellulosic material to be treated and the degree of flame resistance desired in the finished product. Cotton cloth, for example, will meet the U. S. Army flame resistance test given below when impregnated with 10%20%. Smaller quantities on the order of 5%10% may be used where less rigid specifications are imposed. Larger quantities up to 30%-40% may, of course, be used in some cases, but are not generally necessary except when substantial quantities of resinous binder are present in the cloth.

The U. S. Army flame resistance test which was used in evaluating the results described in the following specific examples, is as follows:

Two samples of the impregnated fabric, each 9 x 6 inches, shall be conditioned for not less than 24 hours at a relative humidity of :2 percent and a temperature of :10 degrees F., and then immediately held in a horizontal position over a vertical flame obtained by burning 0.3 ml. of anhydrous ethyl alcohol (absolute) in a flat bottom brass cup. The cup shall be inch outside diameter, inch high overall. The brass used shall be inch thick. The cup shall be supported on material of low heat conductivity such as cork. The center of each sample shall be held 3 inches above the lip of the cup. The alcohol shall be placed in the cup, the cup immediately placed in the test position and the alcohol ignited as soon as possible. The test shall be conducted in a hood or enclosed space so that the test shall not be aflfected by drafts. When conducting repeated tests the air in the hood shall be changed after each test. The test specimens shall remain in the test position until after-glow has ceased. The specimens shall then be measured without removing the fabric from the testing frame. The burned holes shall be measured after the charred area of the fabric has been removed by running a wooden pencil around the inside of the hole and pressing the pencil against the fabric with the long axis of the pencil being perpendicular to the plane of the fabric. The measureemployed to prevent dusting of the guanylmelamine pyroment shall be kenaacmss the longest portion of each awaem 3 hole. In conducting repeated tests sufficient time shall be allowed between tests to permit the cup to cool to room temperature.

Example I A. 7.8 oz. herringbone twill was impregnated with a aqueous solution of guanylmelamine hydrochloride to a 98.5% wet pickup, corresponding to 14.8% of the dry salt based on the dry weight of the cotton fabric, and was dried; The treated twill was then padded through a 10% solution of disodium dihydrogen pyrophosphate and again dried. After ,rinsing excess reagents from the fabric with cold water 14.7% of guanylmelamine pyrophosphate was retained on the fabric. The treated fabric was flame resistant; when a sample was subjected to the standard fiame test, the diameter of the hole was 22 /2.

Example 2 Methylated methylol melamine, unlike diinethylol urea, trimethylol melamine, polyvinyl acetate and other binders, can be applied to the fabric simultaneously with salts of melamine or substituted melamines if desired. Thus, a sample of the cloth described in Example 1 was impregnated with a water solution containing guanylmelamine hydrochloride and 10% methylated methylol melamine, dried at C., and then passed 3 times through a 10% solution of disodiurn dihydrogen pyrophosphate having a pH of 4.0. After drying at 45 C; the fabric was cured 5 minutes at C., washed with warm water'to remove excess reagents, and again dried at 45 C. The hand of the fabric treated by this method was considerably better than that of the fabric of Example 1. i

If desired, the treated fabric may be again impregnated in a solution of methylated methylol melamine, or of dimetliylol urea or other resin, followed by heating to cure the resin on the fabric. Samples treated in this manner with a 5% solution of methylated methylol melamine, dried at 45 C. and cured *5 minutes at 150 C. were submitted to the following wash test:

A piece of fabric 3.5 x 7.5 inches in size was put into a pint stone jar along with .20 steel balls and 200 cc. of an 0.5% soap solution. The jar was then tumbled 45 minutes at F., after which the cloth was removed, rinsed with'water, dried and subjected to the flame test; The results were as follows:

Diameter Original (no wash) 2-2 /z" After 2 washes 2-2 /2 After 5 washes 24%" of the group consisting of pyrophosphoric acid and watersoluble salts thereof and thereby precipitating a guanylmelamine pyrophosphate in said material in finely divided form, the' 'quantity of guanylmelamine so precipitated being within the range of about 10% to 40% based on the weight of the fibrous cellulosic material. I

2, A method according to claim 1 in which the fibrous cellulosic material is then padded in an aqueous solution of methylated methylol melamine, dried, and heated to cure the resin' to its water-insoluble condition.

3. A method of obtaining a washfast; flame-resistant finislfon fibrous cellulosic material which comprises impregnating said material with a water solution containing a water-soluble guanylmelamine salt and also containing a methylated methylol melamine and drying the material and then impregnating it with a member of the group 'consisting of pyrophosphoric acid and water-soluble salts thereof, whereby a guanylmelamine pyrophosphate" is formed, and then heating said material to cure the methylated methylol melamine to its water-insoluble condition, the amount of guanylmelamine so applied being within the range of about 10% to 40% based on the weight of the fibrous cellulosic material.

References Cited in the file of this patent UNITED STATES PATENTS 2,305,035 Rosser Dec. 15, 1942 2,418,525 a Pollak a Apr. 8, 1947 2,421,218 Pollak Mar. 15, 1949 2,464,342 Pollak Mar. 15, 1949 2,488,034 Pingree et al. "Nov. 15,1949 2,519,388 Loukomsky et a1 Aug. 22, 1950 2,520,103 Loukomslty et al. Aug. 22, 1950 2,537,834 Kaiser et al. Jan. 9, 1951 2,537,840 MacLean Jan. 9, 1951 2,582,961 Burnell et a1 Ian. 22, 1952 FOREIGN PATENTS 476,043 Great Britain Nov. 29, 1937 

1. A METHOD OF IMPARTING FLAME RESISTANCE TO FIBROUS CELLULOSIC MATERIAL WHICH COMPRISES IMPREGNATING SAID MATERIAL WITH AN AQUEOUS SOLUTION OF A WATER-SOLUBLE GUANYLMELAMINE SALT AND THEN APPLYING THERETO A MEMBER OF THE GROUP CONSISTING OF PYROPHOSPHORIC ACID AND WATERSOLUBLE SALTS THEREOF AND THEREBY PRECIPITATING A GUANYLMELAMINE PYROPHOSPHATE IN SAID MATERIAL IN FINELY DIVIDED FORM, THE QUANTITY OF GUANYLMELAMINE SO PRECIPITATED BEING WITHIN THE RANGE OF ABOUT 10% TO 40% BASED ON THE WEIGHT OF THE FIBROUS CELLULOSIC MATERIAL. 